Wave signaling system



Sept. 27, 1938. H. .1. M CARTHY 2,131,538

' WAVE SIGNALING SYSTEM Filed Dec. 31, 1936 AAAAIAAA 0 CURRENT POTENTIAL .OIB

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CAPACITY OF CONDENSER [8 IN m-fxt GRID-PLATE CAPACITY IN MMF'D AT IOOOKC.

ATTORNEY Patented Sept. 27, 1938 UNITED STATES P T T OFFICE.

WAVE SIGNALKNG SYSTEM Henry J. McCarthy, Danvers, Massgassignor to Hygrade Sylvania Corporation, Salem, Mass., a

corporation of Massachusetts Application December 31, 1936, Serial No. 118,532

4 Claims.

cation Serial No. 13,047, filed March 26th, 1935.

There is disclosed in said application a system employing a pentode tube of the suppressor grid type wherein the suppressing action is achieved without employing a conductive or metallic connecticn between the suppressor grid and the cathode. The present invention relates to this same type of system and one of its principal ob- 15. jects is to provide a wave repeater or amplifier employing a suppressor grid pentode tube where in the suppressor grid is capable of eifecting suppressor action without conductive connection to the cathode, and at the same time it maintains theinterelectrode capacity between the anode and control grid at a minimum.

A feature of the invention relates to a systememploying a suppressor grid pentode tube wherein the suppressorgrid is insulated from the cathode so far as direct current is concerned, by

a condenser. With this arrangement the suppressor grid acts efficiently to prevent the return of any appreciable number of secondary electrons from the plate or anode to the shield grid, and it also supplements the shield grid in reducing to a desirable minimum, the interelectrode capacity between the anode and the control grid.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims. While the invention will be disclosed herein in schematic form and in connection with certain well-known types of pentode tubes, itwill be understood that this is done merely for explanatory purposes and not by way of limitation thereto. Accordingly in the drawmg,

Fig. 1 is a typical schematic wiring diagram of a system embodying features of the invention.

Fig. 2 is a typical series of characteristic curves showing the relation between plate current and plate voltage in a tube connected according to Fig. 1.

Fig. 3 is a curve showing the relation between the interelectrode control grid-to-plate capacity for different values of the suppressor grid return condenser.

Referring to Fig. 1, the numeral I represents any well-known form of evacuated enclosing envelope either of the metal or glass type. Suitably supported within the envelope is a pentode mount comprising an electron emitting cathode 2 with its insulated heater filament 3; a control grid 4; a shield grid 5; a suppressor grid 6; and an anode or plate-1; It will be understood that any Well-known structure and arrangement of the electrodes may be employed, for example the mount may be similar to that embodied in the tubes designated commercially by the type numi sented for example by tubes of the type 53, 47 and the like.

. The signals to be repeated or amplified are impressed across the control grid 4 and the cathode 2 by any well-known form of signal input coupling circuit represented by the sec- 20,

ondary winding 8 of the coupling transformer.

Preferably the grid 4 is biassed with respect to the cathode by any well-known means, for example by the resistor 9 shunted by condenser 50.

The signal output coupling circuit may be of any 25 suitable type and merely for purposes of explanation it is shown as of the resistance-capacity type in which the plate 1 is connected to the positive potential tap ll through a coupling resistor I2. The potentials across resistor l2 are 0 coupled through capacity 13 to the input of a succeeding stage or to a signal reproducing device, the input terminals of which are represented by numerals I4, l5. In accordance with the usual practice, a leak resistor l6 may be provided. The shield grid 5 is connected to a suitable positive potential tap l'l preferably of a lower voltage than the tap H for purposes well understood in the electron tube art. Heretofore, the suppressor grid 6 has been conductively connected to either the cathode or to ground so as to be at or near cathode potential. This usual conductive connection of the suppressor grid to the cathode, performs. the function of preventing the return of any appreciable number of secondary electrons from the anode to the shield grid, and at-the same time it tends to supplement the shield grid in reducing the interelectrode capacity between the plate and the control grid. As disclosed in my prior application Serial No. 13,047, 50 I have found that the suppressing action of grid 6 may be obtained without a conductive connection to the cathode. In this lattercase, it is necessary to employ a suppressor grid which because of its composition or because of its surface 55 characteristics has the property of emitting few secondary electrons under bombardment either by the primary electrons from the cathode or by secondary electrons. For example as disclosed in said application Serial No. 13,0517 the grid may be coated with ceramic or any other material that has the property of reducing secondary emission as is well known in the electron tube art. With such a grid it is possible to allow it to float, -without any conductive or other connection to the cathode, and the desirable pentode plate current plate voltage characteristics are obtained. I have found however that with this type of suppressor grid floating, While the suppressor action is obtainable, nevertheless the grid does not supplement the shield grid in reducing the interelectrode capacitance. However, I have also found that by returning the suppressor grid to the cathode through a condenser such as condenser l8, it is possible to obtain the suppressing action and at the same time the suppressor grid supplements the shield grid in reducing the interelectrode capacitance. While this method; of suppressorgrid return finds its greatest usefulness in a tube wherein the suppressor grid has a surface capable of inhibiting the emission of secondary electrons, nevertheless it isalso useful as applied to the ordinary type of pentode wherein the suppressor grid is not specially formed or treated to inhibit secondary emission. While the capacitance of condenser I8 is not critical nevertheless it is preferable to employ a condenser having a capacity not materially less than 0.001 mfd., so that the control grid-toplate capacitance is at or near a minimum. Fig. 3 is a curve showing the relation between the interelectrode control grid-to-plate capacity of a type '78 tube for various values of condenser l8. From this it will be seen that the interelectrode capacity rises abruptly for very low values of capacity it. For example if the tube of Fig. 1 is a type 78 tube the condenser l8 should have a capacity of the order of 0.01 mfd. Thus in one particular connection which was found to produce the desired pentode characteristics the control grid 4 was negatively biassed with respect to the cathode and plate current for difierent values of negative bias on the control grid, the curve a being at minus 1 volt, curve b at minus 3 volts, and curve at minus 10 volts. It will be understood of course that various changes and modifications may be made in the various voltages without departing from the spirit and scope of the invention.

What I claim is:

1. In a wave repeater the combination of an electron discharge tube having a cathode, an anode, a control grid, a shield grid and a suppressor grid, means to impress signals on the control grid, means to apply a steady positive potential to the shield grid, and a connection between the supressor grid and cathode to conductively insulate said suppressor grid from the cathode while allowing said suppressor grid to prevent secondary electrons from reaching said shield grid from said anode.

2. In a wave repeater the combination of a pentode tube of the suppressor type, and means to return the suppressor gridto the cathode without a conductive connection thereto, said means comprising a condenser.

3. A wave repeater according to claim 2 in which the condenser has a capacity not materially less than 0.001 mfd.

4. In a wave repeater the combination of a pentode tube of the suppressor grid type, the suppressor grid having its surface specially designed to reduce the emission of secondary electrons therefrom whereby the suppressing action may be obtained while maintaining said suppressor grid conductively insulated from the cathode, and a condenser connected in series between the suppressor grid and the cathode to allow said suppressor grid to supplement the shield grid in reducing interelectrode capacitance.

HENRY J. MCCARTHY. 

